Environmental concerns pertaining to utilization of fossil fuels to generate electric power together with the non-renewable nature of such fossil fuels have increased demand for alternative energy sources. Exemplary electric power systems that utilize renewable energy resources include solar power systems, wind power systems, hydroelectric power systems, geothermal power systems, amongst others.
Conventional solar power systems, particularly those utilized to provide electric power to a residence, include solar panels that comprise a plurality of relatively large silicon photovoltaic cells (e.g., approximately six inches by six inches). For instance, a single solar panel can include approximately seventy two cells. The solar cells are manufactured to output a certain voltage (e.g., 0.6 volts for silicon cells) that is approximately constant regardless of an amount of solar radiation of particular wavelengths received at the solar cells, and are electrically connected in series within a solar panel, such that the solar panel produces approximately 40 volts. A typical residential solar system includes several solar panels (e.g., 5-10), and the panels are electrically connected in series, thereby resulting in several hundred cells being electrically connected in series that, collectively, output a voltage that is approximately equal to the sum of the voltages of the individual cells. It is to be noted, however, that when solar cells and panels are arranged electrically in series, the current must be equal across each of the cells in each of the solar panels.
Since the current of a photovoltaic cell is proportional to the light that is incident on the cell, if one cell of a series connection receives a low light level, the entire series connection has a low current. Thus, a typical solar power system configuration that includes several solar panels can have a severe current reduction (and power output reduction) when one cell or a portion of a cell has a low light level (e.g., due to shading). Oftentimes, when solar power systems are installed on residences or other buildings, trees or other obstructions may be nearby, and accordingly, shading of at least a portion of a module can occur frequently.
When shading occurs across a solar power system in a certain pattern, unless protective electric devices are in place, solar cells can be severely damaged. For instance, if a single solar cell is shaded by an obstruction, and all other cells in the solar power system are illuminated, then the single cell can be driven into reverse breakdown to support the current flow generated by the other cells. In current solar power installations, cell current is approximately five amperes, and silicon cells have a breakdown voltage of approximately 60 volts or more, depending on the cell design and manufacture techniques used to produce the cell. As breakdown is not a uniform process across a large cell, the relatively large current (five amperes) and the relatively large power (upwards of one hundred watts) can cause the device to malfunction in either a shorted or open state, causing improper operation and permanent damage to the cell, panel, and/or installation.
To prevent photovoltaic cells in solar power installations from being driven into reverse breakdown, bypass diodes are selectively positioned across the cells, thereby diverting current from cells with no photocurrent and preventing such cells from entering the breakdown region. Utilization of bypass diodes, however, consumes space in a solar power installation, is relatively expensive, and increases assembly time of solar panels. Furthermore, using bypass diodes can result in excessive power production loss, since each bypass diode normally protects one third of the cells in a panel (e.g., there are usually three bypass diodes in a panel). Therefore, if one cell is shaded, power production from all of the cells covered by the bypass diode will be lost.